JP2725933B2 - Auto focus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto-focusing device, and more particularly, to an image-taking device such as a video camera having an auto-focus function, which automatically focuses on a subject based on a video signal obtained from an image sensor. The present invention relates to an autofocus device.

[0002]

2. Description of the Related Art Conventionally, in an autofocus device used for an image pickup device such as a video camera, a method has been developed in which a video signal itself obtained from an image pickup device is used to evaluate a focus control state. In such a way,
There is essentially no parallax, and it has many excellent features such as accurate focusing even when the depth of field is shallow and the subject is located at a distance. Moreover, according to this method, there is no need to separately provide a special sensor for autofocus, and the mechanism is extremely simple.

As an example of such a focus control method using a video signal, a control method called a so-called hill-climbing servo method has been conventionally known. An autofocus apparatus using the hill-climbing servo system is described in, for example, Japanese Patent Application Laid-Open No. Sho 63-215268 (H04N 5/232). The focus evaluation value is detected, the focus evaluation value is constantly compared with the value one field before, and the focus lens position is continuously vibrated minutely so that the focus evaluation value always takes the maximum value.

By the way, the level of the video signal obtained from the imaging device is usually set to 50% or less of the dynamic range of the imaging device in order to prevent the video signal level from saturating in the high luminance portion of the subject. I have.

[0005] For example, in a consumer video camera, generally, the dynamic range of a CCD as an image pickup device is 1/1 of the dynamic range.
3 so that a video (luminance) signal having a level of 100 IRE is obtained when light having a luminance corresponding to 3 is incident.
The output signal level of D is set (about 1/6 in the case of a commercial imaging device).

That is, the output of the CCD is 10 bits A /
When D conversion is performed, the range of values (dynamic range) that the digital output of the CCD can take is 0 to 1023,
In this case, the value taken by the digital video signal having the luminance level of 100 IRE is about 340. The average value of the luminance level of the video signal in a normal shooting state is 60 to 70
Since the value is about IRE, the value taken by the digital video signal in this case is about 200 to 250.

[0007]

As described above, in the conventional image pickup apparatus, since the level of the picked-up video (luminance) signal is set low, the level of the high-frequency component extracted for the auto-focus operation is also low. Therefore, there is a problem that the accuracy of focusing is reduced.

More specifically, when photographing an object having a particularly low luminance, the contrast of the object is reduced as a whole, and the level of the high-frequency component extracted for the hill-climbing control is reduced. As a result, the detected focus evaluation value also decreases, and the accuracy of detecting the maximum value decreases. Therefore, it is difficult to find the in-focus position with high accuracy, and this has caused a malfunction of the autofocus operation.

On the other hand, even in the case of a normal subject having relatively high luminance, the range of the luminance signal digitized as described above corresponds to only about 1/3 of the entire dynamic range of the CCD. The high-frequency component level taken out due to the above is not a sufficiently large value. Therefore, even when a subject of normal brightness is photographed, the accuracy of focusing is not always high, and there is a problem that a malfunction of the autofocus operation may occur.

An object of the present invention is to provide an autofocus apparatus which can always perform an autofocus operation with high accuracy regardless of the luminance of a subject.

[0011]

SUMMARY OF THE INVENTION The present invention, in summary, is an auto-focusing apparatus for automatically adjusting the focus on a subject based on a video signal obtained from an imaging means having a focus lens and an imaging device. Relative position changing means for changing the relative position of the focus lens with respect to the image sensor in the optical axis direction; nonlinear processing means for independently performing nonlinear processing on a video signal obtained from the imaging means; High-pass filter means for extracting a high-frequency component of the processed video signal, and a focus evaluation value for detecting the level of the extracted high-frequency component and taking a maximum value at a focus position at regular intervals. Focus evaluation value detecting means for converting the focus evaluation value and sequentially supplying the focus evaluation value, and the focus evaluation value becomes the maximum value in response to the focus evaluation value supplied from the focus evaluation value detecting means. The location, and a control means for controlling the relative position changing means to move the relative position of the focus lens, the luminance level detection means for detecting a brightness level of an image signal obtained from an imaging device. The non-linear processing means has an input / output characteristic that is substantially linear or nearly linear for a relatively high-brightness subject in accordance with the detected brightness level, and for a relatively low-brightness subject. Changes the input / output characteristics so as to have an input / output characteristic that increases the gain when the input level is low and decreases the gain when the input level is high.

[0012]

In the autofocus device according to the present invention, the video signal is independently subjected to nonlinear processing for the autofocus operation, and the input / output characteristics of the nonlinear processing are changed according to the luminance level of the video signal. The high-precision autofocus operation can always be performed irrespective of the luminance of the subject and without affecting the original signal processing of the video signal.

[0013]

FIG. 1 is a schematic block diagram showing a video camera provided with an autofocus device according to one embodiment of the present invention. In FIG. 1, the video camera includes a focus lens 1, a focus ring 16 for moving the lens 1 forward and backward, a focus motor 15 for driving the focus ring 16, and an imaging device 2 such as a CCD. Here, the focus lens 1 may be moved forward and backward using a piezoelectric element instead of the focus motor 15, or the image pickup element 2 itself may be moved forward and backward instead of the focus lens 1.

An image formed on the image pickup surface of the image pickup device 2 by the focus lens 1 is photoelectrically converted by the image pickup device 2 and given to the preprocessing circuit 3 as a video signal. The preprocessing circuit 3 performs predetermined processing such as noise removal and gain adjustment on the given video signal, and then provides the same to the A / D converter 4.

The video signal digitized by the A / D converter 4 is separated into a chrominance signal C and a luminance signal Y by a Y / C separation circuit 5 and further supplied to a gamma circuit 6. The gamma circuit 6 performs predetermined processing such as gamma correction on the given signal, and then gives the signal to the encoder 7.
The encoder 7 receives the supplied color signal C and luminance signal Y
Is converted into a video signal conforming to a predetermined television system, and given to the D / A converter 8. And the D / A converter 8
Color signal C and luminance signal Y analogized by
Is supplied as an analog imaged video signal and recorded on a magnetic recording medium (not shown) or externally output.

On the other hand, the luminance signal Y output from the Y / C separation circuit 5 is also supplied to the nonlinear circuit 9 at the same time. The configuration and operation of the nonlinear circuit 9 will be described later in detail. The luminance signal Y subjected to the non-linear processing by the non-linear circuit 9 is provided to a high-pass filter (HPF) 10, which extracts a high-frequency component of the luminance signal Y.

Since the output of the HPF 10 has positive and negative values, it is supplied to an absolute value converting circuit 11 to be converted into an absolute value. For example, considering the case where the output of the HPF 10 is represented by a two's complement, when the most significant bit (sign bit) of the output of the HPF 10 is 0, that is, when the input data to the absolute value conversion circuit 11 is a positive number, In some cases, the absolute value conversion circuit 11 outputs the input data as it is, and when the most significant bit is 1, that is, when the input data is a negative number, the absolute value conversion circuit 11 inverts the bit of the input data and further outputs 1 bit. Is output. At this time, if an error is allowed, the addition of 1 can be omitted.

The output of the absolute value conversion circuit 11 is
a, the integrating circuit 12a integrates, for each field period, a portion corresponding to a specific area on the screen, of the high-frequency component converted into an absolute value as described above, for each field period. Is output. The integration result S1 is provided to the focus detection circuit 13 as a focus evaluation value. Note that the integrating circuit 1
Details of 2a will be described later in detail.

The focus detection circuit 13 is a circuit for performing the above-described hill-climbing control, and includes the focus evaluation value S1 output from the integration circuit 12a and the motor position detection circuit 17
A control signal is generated in accordance with the rotational position of the focus motor 15 detected by the control unit and is given to the focus motor drive circuit. Thus, the rotation of the focus motor 15 is controlled such that the relative position of the focus lens 1 moves to a position where the focus evaluation value S1 takes a local maximum value. Such hill-climbing servo control is well-known as described above, and therefore will not be described in further detail here.

Further, the luminance signal Y output from the Y / C separation circuit 5 is directly applied to another integration circuit 12b. The integration circuit 12b integrates a portion corresponding to the above-described specific region in the given luminance signal Y for each field period, and outputs an integration result S2. The integration result S2 is provided to the focus detection circuit 13 as an illuminance evaluation value. The focus detection circuit 13 supplies a control signal to the nonlinear circuit 9 according to the illuminance evaluation value, that is, according to the brightness of the subject in a specific area of the screen, and changes the input / output characteristics of the nonlinear circuit 9.

FIG. 2 is a graph showing an example of a change in the input / output characteristics of the nonlinear circuit 9. Referring to FIG. 2, when photographing a very bright (high-brightness) subject, the input / output characteristics of nonlinear circuit 9 change according to the control signal from focus detection circuit 13 in FIG. The input / output characteristics are switched as shown in ()). That is, for a high-luminance subject, it is considered that the level of the luminance signal Y is present to a very high level. In such a case, to avoid saturation of the luminance signal level, (a) The input / output characteristics that the output does not saturate as shown by are used.

On the other hand, when photographing an object of normal brightness, the input / output characteristics of the non-linear circuit 9 depend on the focus detection circuit 1
(B) or (d) of FIG. 2 according to the control signal from
The input / output characteristics are switched as shown in FIG. That is, in this case, since the level of the luminance signal Y falls within the range of about 1/3 of the dynamic range of the image sensor 2, when the luminance level is low, the gain of the nonlinear circuit 9 is increased and the luminance is increased. The input / output characteristic of (b) or (d) is used so that the output level of the nonlinear circuit 9 is increased as a whole by reducing the gain when the level is high.

Further, when a dark (low-brightness) object is photographed, the input / output characteristics of the non-linear circuit 9 depend on the control signal from the focus detection circuit 13 (c) or (e) in FIG. The input / output characteristics are switched as shown in FIG. That is,
In this case, the output level of the nonlinear circuit 9 is increased as a whole by further increasing the gain of the nonlinear circuit 9 when the luminance level is low.

FIG. 3 is a block diagram showing an example of the nonlinear circuit 9 having variable input / output characteristics as shown in FIG. In FIG. 3, the selector 23 includes a plurality of combinations of constant values (1a, 2a,..., N) in accordance with a control signal supplied from the focus detection circuit 13 of FIG.
a), (1b, 2b, ..., nb), ..., (1x, 2x,
.., Nx) are given to the selector 24 as a combination of n coefficient values.

On the other hand, the selector 25 also performs a combination of a plurality of sets of constant values (1a, 2a,..., Na), (1) in accordance with a control signal supplied from the focus detection circuit 13 via the terminal 22.
b, 2b, ..., nb), ..., (1x, 2x, ..., nx)
Is given to the selector 26 as a combination of n coefficient values.

The luminance signal Y input from the Y / C separation circuit 5 of FIG. 1 via the terminal 21 is supplied to one input of a multiplier 27 and to a range comparator 22.
The range comparator 22 generates a selection signal according to the value of the luminance level, and supplies the selection signal to the selection inputs of the selectors 24 and 26.

The selector 24 operates in response to the selection signal,
One coefficient value is selected and given to the other input of the multiplier 27.
The result of this multiplication is further applied to one input of an adder 28. Further, the selector 26 selects one coefficient value as an offset value in accordance with the selection signal and supplies the same to the other input of the adder 28.

The result of this addition is output from the terminal 30 via the overflow clip circuit 29. This allows
According to the luminance level, the input luminance signal is multiplied by a constant coefficient, and a constant offset value is further added. As a result, a nonlinear input / output characteristic consisting of n polygonal lines as shown in FIG. 2 is obtained. Become.

FIG. 4 is a block diagram showing another example of the configuration of the nonlinear circuit 9. The nonlinear circuit 9 shown in FIG. 4 includes a plurality of ROs in which different input / output characteristic data are written.
M33-1, 33-2,..., 33-n, and a non-linear output is output to each ROM by using the luminance signal level Y input from the Y / C separation circuit 5 of FIG. And is supplied to the selector 34. The selector 34 selects one ROM output in accordance with a control signal input from the focus detection circuit 13 of FIG. 1 via the terminal 32 and supplies it from the terminal 35 as a non-linear output.

FIG. 5 is a circuit diagram of the integrating circuit 12 shown in FIG.
It is a block diagram which shows the example of a structure of a or 12b. In the example shown in FIG. 5, it is assumed that a plurality of evaluation values are obtained from a plurality of regions set on the screen.
In FIG. 5, a horizontal counter 49 counts a system clock supplied from a signal source (not shown) via a terminal 42 and is reset by a horizontal synchronization signal supplied via a terminal 43 from a signal source (not shown). It is. The output of the horizontal counter 49 is given to the area decoder 51 as a horizontal address.

On the other hand, the vertical counter 50 counts the above-mentioned horizontal synchronizing signal, and outputs a signal from a signal source (not shown) to the terminal 4.
4 is a counter which is reset by a vertical synchronizing signal supplied through the counter 4. The output of the vertical counter 50 is given to the area decoder 51 as a vertical address. The area decoder 51 outputs a plurality of area signals that do not overlap with each other in accordance with these horizontal and vertical addresses, and supplies the area signals to one input of each of a plurality of AND gates forming the gate circuit 52. The selection input is given as a selection signal.

On the other hand, the data input via the terminal 41 is given to one input of an adder 45, and the output of the adder 45 is a register consisting of n registers provided corresponding to each area on the screen. It is provided to the circuit 46 in parallel. Further, in response to the area signal from the area decoder 51, the selector 47 selects one of the outputs of the n registers and supplies it to the other input of the adder 45. The adder 45, the register circuit 46, and the selector 47
It constitutes the integrating circuit 12a or 12b in the figure.

Further, the system clock inputted through the terminal 42 is supplied to a plurality of AND gates constituting the gate circuit 52.
Commonly applied to the other input of each of the gates. Therefore, the integrating circuit integrates the input data for each area using the register corresponding to each area designated according to the area signal output from the area decoder 51.

In this manner, the input data is integrated over one field period for each area, and thereafter held in the register circuit 48 composed of n registers which receives the vertical synchronization signal supplied from the terminal 44 as a clock input. , And supplied to the focus detection circuit 13 as an evaluation value of each area.

[0035]

As described above, the autofocus device according to the present invention includes a relative position changing means for changing a relative position of the focus lens in the optical axis direction with respect to the image pickup device, and a video signal obtained from the image pickup means. Nonlinear processing means for performing nonlinear processing independently, high-pass filter means for extracting high-frequency components of the video signal subjected to nonlinear processing by the nonlinear processing means, and detecting the level of the extracted high-frequency component A focus evaluation value detecting means for converting the focus evaluation value to a maximum value at the in-focus position and sequentially supplying the focus evaluation value at predetermined intervals, and a focus evaluation value supplied in response to the focus evaluation value supplied from the focus evaluation value detection means. Control means for controlling the relative position changing means so as to move the relative position of the focus lens to a position where the value becomes the maximum value; and a luminance level of a video signal obtained from the imaging means. And a non-linear processing means having substantially linear or nearly linear input / output characteristics for a relatively high-luminance subject in accordance with the detected luminance level. By changing the input / output characteristics of a relatively low-luminance subject so as to have input / output characteristics such that the gain is increased when the input level is low and the gain is decreased when the input level is high. Therefore, the autofocus operation can always be performed with high accuracy regardless of the luminance of the subject and without affecting the original processing of the video signal.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a video camera provided with an autofocus device according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of input / output characteristics of the nonlinear circuit illustrated in FIG. 1;

FIG. 3 is a block diagram illustrating an example of a nonlinear circuit illustrated in FIG. 1;

FIG. 4 is a block diagram illustrating another example of the nonlinear circuit illustrated in FIG. 1;

FIG. 5 is a block diagram illustrating an example of an integrating circuit illustrated in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Focus lens 2 Image sensor 3 Preprocessing circuit 4 A / D converter 5 Y / C separation circuit 6 Gamma circuit 7 Encoder 8 D / A converter 9 Nonlinear circuit 10 HPF 11 Absolute value conversion circuit 12a, 12b Integration circuit 13 combination Focus detection circuit 14 Focus motor drive circuit 15 Focus motor 16 Focus ring 17 Motor position detection circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Yamamoto 2--18 Keihanhondori Moriguchi City Sanyo Electric Co., Ltd. (72) Inventor Haruhiko Murata 2-18 Keihanhondori Moriguchi City Sanyo Electric Co., Ltd. ( 56) References JP-A-60-142678 (JP, A) JP-A-3-243307 (JP, A)

Claims (1)

(57) [Claims] 1. An auto-focusing apparatus for performing automatic focusing of a focus on a subject based on a video signal obtained from an imaging unit having a focus lens and an image sensor, wherein an optical axis direction of the focus lens with respect to the image sensor. Relative position changing means for changing a relative position of the image signal; nonlinear processing means for independently performing nonlinear processing on the video signal obtained from the imaging means; and a video signal subjected to nonlinear processing by the nonlinear processing means. High-pass filter means for extracting the high-frequency component of the detected high-frequency component, detecting the level of the extracted high-frequency component, and converting the detected level to a focus evaluation value having a maximum value at a focal point position at regular intervals, and sequentially supplying the focus evaluation value. Focus evaluation value detecting means, and the focus evaluation value becomes a maximum value in response to the focus evaluation value supplied from the focus evaluation value detecting means. A control unit for controlling the relative position changing unit so as to move a relative position of the focus lens; and a luminance level detecting unit for detecting a luminance level of the video signal obtained from the imaging unit. The non-linear processing means has an input / output characteristic that is substantially linear or nearly linear for a relatively high-luminance subject according to the detected luminance level, and for a relatively low-luminance subject. An autofocus device that changes input / output characteristics so as to have input / output characteristics such that the gain is increased when the input level is low and the gain is decreased when the input level is high.